Abstract

The 1967 Caracas earthquake followed some of the most significant earthquakes that have occurred in this century. These included the 1960 earthquake in Chile, the 1962 earthquake that affected Mexico City, the 1964 Great Alaska, the 1964 Niigata and the 1966 Parkfield earthquakes. Each of these of earthquakes had its own signature and each contributed to our understanding of the effects of earthquakes on soils (e.g., the massive landslides in 
Alaska, liquefaction in Niigata … etc) and to our awareness that these effects need to be incorporated into rehabilitating existing conditions and in future designs. The effects of local site conditions on earthquake ground motions, however, were not acknowledged as explicitly. In fact, except for a few countries (e.g., Chile and Turkey), these effects were not included in the building codes at that time. While the difference in performance of structures in Mexico City was attributed to the effects of local site conditions on earthquake ground motions experienced by these structures, it was suggested that there is a "bowl of jelly" underlying that part of Mexico City which contributes to the amplifications of these motions. The 1967 Caracas earthquake showed that variations of damage to structures can be directly related to the interacting effects of the characteristics of the structure and the underlying subsurface conditions. 

Probably the most detailed evaluations of the relationship between building damage and local soil conditions were those conducted immediately after the 1967 Caracas earthquake. These evaluations led to the conclusion that the depth and characteristics of the soils underlying the site have a significant effect on the characteristics of the ground motions experienced at that site and hence on the potential for damage of the building itself, as illustrated in the figure below. 

These findings were very instrumental in encouraging adoption of local site factors in building codes, particularly after the occurrence of the 1971 San Fernando earthquake, which exhibited similar, albeit less dramatic, pattern of damage to buildings. The earthquakes that have occurred since the 1971 San Fernando earthquake, have all shown that earthquake ground motions are affected by local site conditions. Our understanding of these effects from the geotechnical engineering perspective as well as based on seismological considerations have increased markedly over the past several years. 

Relationship between Structural Damage Intensity and Soil Depth in the 1967 Caracas Earthquake (after Seed et al, 1972; Seed & Alonso, 1974) 

My discussions during this commemeration of the 1967 earthquake will cover these aspects as well as a brief review of the state of the art regarding the evaluation of the response of soil sites during earthquakes using numerical as well as physical modeling..

References

Seed, H. B., Whitman, R. V., Dezfulian, H., Dobry, R., and Idriss, I. M. (1972), "Soil Conditions and Building Damage in 1967 Caracas Earthquake", Journal of Soil Mechanics and Foundations Division, ASCE, v. 98, no. SM8, August 1972, pp 787- 806.

Seed, H. B. and Alonso, G. (1974), "Effects of Soil Structure Interaction in the Caracas Earthquake of 1967", Proceedings, First Venezuelan Conference on Seismology and Earthquake Engineering, October.